Objectives. To determine frequency and clinical criteria associated to the inadequate indication of blood products. Materials and methods. A cross-sectional study was performed between June and October 2002. Clinical charts and the laboratory tests from patients receiving blood transfusions were examined. A blood transfusion guideline was elaborated based on published consensus, and used to determine whether the indications for blood products transfusion was adequate or inadequate. Results. A total of 311 blood transfusions were evaluated. The global prevalence of inappropriate indication was of 33.8 %. Red blood cells (RBC) were used inappropriately in 25 %, fresh frozen plasma (FFP) in 59 %, platelets in 13 % and cryoprecipitate in 88 %. From surgery related transfusions half of the indications were inadequate. In internal medicine, ICU and emergency related transfusions, approximately one third of the indications were inadequate. The FFP is the worst used blood product. Conclusions. We found a high frequency of inadequate blood transfusion. The identification of the specific clinical criteria used in inadequate indications transfusions will help in designing a better educational strategy towards a more rational use of the blood products.